When using WooCommerce Payments, you have two options to sell subscription products:
When using the subscriptions functionality built-in to WooCommerce Payments, subscription purchases can only be processed via WooCommerce Payments. Other payment gateways will not be available on checkout when a subscription product is in the cart if the WooCommerce Subscriptions extension is not active.
If WooCommerce Payments is installed but disabled as a gateway, customers with subscriptions in the cart will see a notice saying there are no payment gateways available on checkout.
To allow customers to purchase subscriptions with another gateway, you will need to purchase the WooCommerce Subscriptions extension.